Internal Defects Steel Weld Repair

Porosity of the weld metal at high temperatures, excessive absorption of the gas (e.g., H2) or because the bath inside the metallurgical reaction gases (e.g., CO), the bath is cooled and solidified in the time to discharge, and in the inside or the surface of the weld cavities, namely pores. The presence of pores reduces the effective work weld cross section, decreasing the mechanical strength of the joint. If penetrating pores or continuity exists, it will seriously affect the tightness of the weldment. After the welding process, cracks or welding, metal in the welded joint region appears is called a partial fracture cracks. Cracks may occur in the weld may also be generated on both sides of the weld heat affected zone. Sometimes produced in the metal surface, the metal may be generated internally.
Generally in accordance with the mechanism of crack formation, which can be divided into two types of thermal cracking and cold cracking. Thermal cracking is generated by a liquid to a solid state crystallization process in the weld metal, mostly produced in the weld metal. The main cause of the existence of the low-melting substances (such as FeS, m.p. 1193 ) weld which weakens the contact between the grains when subjected to high welding stress, it is easy to cause breakdown between the grains. Weldments and welding rod containing S, Cu impurities such a long time, it is prone to hot cracking. Thermal cracks along the grain boundary characteristic distribution. When the crack through the surface and the outside world, the tendency has obvious hydrogenation. Cold cracks are generated in the cooling process after welding, mostly produced in the base metal or base metal and the weld at the junction of the fusion line. The main reason is due to the generation of weld heat affected zone or formed within the quenched structure, under high stress, caused by the rupture of the grains, when welding high carbon content of the alloying elements more easily or hardened steel, the prone to cold cracking. Excessive weld melt into hydrogen, can cause cold cracking. Crack is the most dangerous kind of defect, which in addition to reducing carry-section outside, but also have serious stress concentration in the use of crack will gradually expand, may eventually lead to the destruction member. So welded structures generally do not allow the existence of such defect , a shovel was found to be necessary to re-welding.